The relation between swelling properties and enzymatic degradation of azo polymers designed for colon-specific drug delivery.

Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA), and terpolymers of HEMA, MMA, and methacrylic acid (MA) were synthesized in the presence of N,N'-bis(methacryloyloxyethyloxycarbonylamino)azobenzene (B(MOEOCA)AB) and evaluated as coating materials for colonic targeting. The release of ibuprofen, a model drug, from capsules coated with the azo polymers was investigated in vitro. The release medium was made up of sonicated rat cecal content, benzyl viologen, glucose-6-phosphate, glucose-6-phosphate dehydrogenase, and nicotine amide dinucleotide phosphate (NADP) in phosphate buffer (pH 6.8, 0.05M). The drug-release profiles indicate that the degradation of the azo polymer coatings depends on their degree of swelling, due to a higher accessibility of the azo bonds for the bacterial azo reductase. The best results were obtained with azo polymers containing MA: 98.7 (+/- 1.1) % of ibuprofen was released after 19 hours residence in the release medium, while only 26.2 (+/- 4.9) % in the control experiment. These findings demonstrate that azo polymers are promising materials for delivering drugs selectivity to the colon.